Sleep etiology: structure and characteristics

DREAM, a condition that periodically occurs in humans and other warm-blooded animals, in which motor and sensory activity is interrupted.During sleep, sensitivity is reduced, many muscles relax, reflexes are inhibited.Sleep differs from dreamlike states — coma, anesthesia, hibernation, or hypnosis — in that it occurs under the influence of internal, not external factors, and it retains the ability to wake up.

The nature of sleep has always aroused heightened interest and served as a reason for many guesses and assumptions.This is not surprising, since a person spends a third of his life in a dream.In ancient cultures, there were various deities who patronized sleep.In Greek mythology, the god of sleep was called Hypnos, in Roman – Somnus .Morpheus, the god of dreams, was one of the thousand sons of Somnus .The god of sleep was considered the brother of the god of death, and both were sons of the goddess of night.

Modern research has greatly enriched our ideas about sleep.Special conditions are created in laboratories engaged in the study of sleep, allowing to evaluate the effect on sleep of certain factors (experimental variables).Studies are carried out indoors with sound insulation and controlled temperature, and the data obtained are based on objective measurements and continuous monitoring.Monitoring is usually performed at night for 8 hours and includes recording of the electrical activity of the brain (electroencephalogram, EEG), eye movements (electrooculogram, EOG), and muscle activity (electromyogram, EMG).Such studies are important for the diagnosis and treatment of sleep disorders, as well as for analyzing the effects of drugs on the central nervous system.

One of the first and most important results of laboratory research was the discovery that a sleeping person periodically has rapid eye movements during the night .The sleep phase, during which rapid eye movements are recorded, was called “fast” (or paradoxical) sleep or sleep with fast eye movements;in this phase, the person most often sees dreams.The remaining stages of sleep, during which no rapid eye movements are observed, were collectively called “slow” sleep or sleep withoutquick eye movements.

Phases of sleep.

Slow sleep, in turn, consists of separate stages.They are referred to as the 1st, 2nd, 3rd, and 4th stages.Fast sleep is not divided into separate stages and is considered as a single phase.

In humans, stage 1 is associated with the process of falling asleep.At this time there is a modification of the alpha rhythm on the electroencephalogram.In a state of relaxed wakefulness, an alpha rhythm is detected with a frequency of 8–12 cycles per second.As you fall asleep, the alpha waves gradually disappear, giving way to low-amplitude high-frequency activity.BDG is absent.

The transition from wakefulness to sleep is accompanied by a repeated feeling of swimming , often interrupted by a sudden start, which again awakens a person.This sudden jerk is called myoclonic jerking.The significance of such twitching is unknown, but it is believed that it may be an activation reaction to a significant, albeit weak, external stimulus.

The first stage quickly passes into the second.At this moment, electroencephalograms usually register flashes of activity at a frequency of 12–16 cycles per second (“sleep spindles”), which alternate with background low-amplitude activity.For the 3rd stage is characterized by the presence ofelectroencephalograms of high-amplitude slow waves with a frequency of 1-3 cycles per second, sometimes combined with “sleepy spindles”.In the 4th stage, at least half of the time, high-amplitude slow waves dominate.

Phase with rapid eye movements, in addition to rapid eye movements, is characterized by a characteristic picture.N- electroencephalogram, low amplitude fast activity that resembles in many wayselectroencephalogram in a person who is in a state of active wakefulness.

Sleep structure

In people of young age, as they fall asleep, an initial (or descending) 1st stage appears.Then the 2nd, 3rd and 4th stages successively replace each other.This is followed by a reverse transition from the 4th stage through the 3rd and 2nd stage in the phase of REM sleep.It passes to the 2nd stage, then the 3rd, 4th, 3rd, 2nd stages come, and finally, the phase with rapid eye movements appears again.This cycle, beginning at stage 2 and ending in a phase with rapid eye movements, is regularly repeated throughout the night.The only exceptions are later, predawn cycles, which usually do not include the 4th stage — sleep only deepens to the 3rd stage, followed by the 2nd stage and the REM phase .

The cycle duration is such that the phase with rapid eye movements occurs on average every 70–90 minutes.At the same time, the first 75–100 min of sleep is occupied by sleep without fast eye movements (mainly the 3rd and 4th stages).Due to the long initial period of sleep without fast eye movements , as well as the gradual increase in the duration of sleep with BDG with each new cycle, this phase of sleep takes longer in the second half of the night.

Every night, sleep with rapid eye movements appears four to six times, depending on the duration of sleep, and not on the individual characteristics of the person.The first sleep period with quick eye movements lasts about 10 minutes, and the last – 20–35 minutes.In general, sleep with rapid eye movements takes about 20% of the total sleep time.

In infants, the total duration of REM is highest.In preterm sleep with rapid eye movements, it takes 60–80% of the total sleep time, and in full-term sleep – 40–50%.Constantly, the proportion of sleep with rapid eye movements decreases and by about the eighth month of a child’s life drops to 20–25%.This level is maintained with minor deviations throughout life.

The sleep cycle of a newborn lasts from 50 to 60 minutes.During periods of sleep with rapid eye movements, frequent sucking movements, slight twitching, grimaces, tremors, and smiles are observed.Unlike adults, newborns can directly transition from waking to sleeping with quick eye movements.

In infants and children of the first year of life, the 3rd and 4th stages are extremely rare.In older children, the duration of these stages increases in the initial period of sleep, whereas the first period of sleep with rapid eye movements appears only two to three hours after falling asleep.The main difference in the structure of sleep in children, adolescents and young people is reduced to a progressive decrease as the duration of the 3rd and 4th stages grows.

Compared with young people, in healthy elderly people, the overall sleep time is reduced, the frequency of awakenings is increased, sleep with rapid eye movements is more often interrupted, and there is a significant decrease or disappearance of the 4th stage.In old age, there is a tendency to return the structure of sleep, characteristic of children, with a tendency to drowsiness in the daytime and more frequent nighttime awakenings.

CHARACTERISTICS OF SLEEP

Dreams.

One of the cardinal discoveries in the field of sleep research was the fact that in 80% of cases, people who were awakened in a phase with rapid eye movements told about dreams.The same people who were woken up in the phase withoutrapid eye movements, rarely talked about dreams.Mental activity recalled by people who are awakened during sleep withoutthe rapid movements of the eyes were more like thoughts than of sleep, because there were no living pictures characteristic of dreams associated with their own experiences.

Since sleep with rapid eye movements cyclically occurs throughout the night for all people, those people who say they never dream can most likely simply not be able to remember them.Sleep with rapid eye movements does not occur under the action of any internal or external stimuli – it is generated by internal mechanisms at some point in a cycle lasting about 90 minutes.But if the stimulus acts during sleep with rapid eye movements, it may be reflected in the content of the dream.

Other studies have shown that people who woke up during sleep with quick eye movements in the second half of the night tell about their dreams better.The dream report also depends on how the person was awakened — suddenly or gradually, and also for how long a wake-up occurred in relation to sleep with rapid eye movements.With a gradual awakening, the story is more abstract and less vivid.In addition, remembering sleep is reduced in direct proportion to the time that has elapsed from the end of the sleep phase with rapid eye movements before waking up.

Sleep depth

is determined primarily by two factors: the stage of sleep and the time of night.The deepest sleep, characterized by the highest threshold of awakening, is observed during the 4th stage – it is during this period that the person is most difficult to wake up.During sleep with rapid eye movements, the threshold for awakening is lowest, and therefore it is easiest to interrupt this sleep.However, it should be noted that not all stimuli equally contribute to waking up during sleep with rapid eye movements.As for the time of night, it is more difficult to wake up a person at any stage of sleep at the beginning of the night than at the same stage in the second half of the night.

During sleep with fast eye movements , as a rule, there is an acceleration of physiological and metabolic processes, which manifests itself very diversely.Pulse and respiration rates, as well as blood pressure, are subject to significant fluctuations during sleep with rapid eye movements, and brain temperature, oxygen consumption and total nerve cell activity increase.The contrast to this increase in functional activity is a pronounced decrease in muscle tone during sleep with rapid eye movements.During these same periods, erection of the penis often occurs, which begins and ends synchronously with their beginning and ending.

Neurochemistry.

The onset of sleep and its individual stages is associated with the activity of a complex network of nerve structures that functions through various neurotransmittersistemaAktivnost brain structures that use serotonin as a neurotransmitter , has a significant impact on the occurrence and maintenance of sleep without rapid eye movements, and also determines the transition to sleep with rapid eye movements.Another, so-called.The adrenergic system, consisting of neurons producing adrenaline-like substances norepinephrine and dopamine, initiates, as it is believed, the tonic and phase sleep components with rapid eye movements.The tonic component, detected on EMG as a decrease in the parameters of muscular activity, includes relaxation of the facial muscles, and the phase component includes intermittent flashes of rapid eye movements.

During sleep, the content of corticosteroids (hormones of the adrenal glands) in the blood and urine rises, reaching a peak in the second half of the night, when sleep with rapid eye movements prevails.A close connection between the 24-hour sleep-wake cycle and the secretion of certain hormones of the hypothalamic-pituitary system (hypothalamus and pituitary – brain structures located at its base) is also revealed.It is essential that these hormones are regulated by the same biogenic amines (serotonin, norepinephrine, dopamine) as the neural mechanisms responsible for sleeping with or without rapid eye movements.quick eye movements.Growth hormone is secreted during the first two hours of sleep, mainly during the 3rd and 4th stages.The content of prolactin (in both men and women) peaks in the last one or two hours of sleep.

The secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in different phases of sleep changes with age.Before puberty, the level of LH in children remains unchanged during the day, whereas after the onset of puberty, periodic LH secretion occurs only during sleep, and not during wakefulness.In adult men, both LH and FSH are secreted throughout the day periodically with a slight increase in LH levels towards the end of sleep, when sleep with rapid eye movements dominates.

Neuroanatomy.

At present, it is known that the activity of the cortex cells detected on the electroencephalogram and the state of wakefulness are maintained by the ascending reticular activating system (reticular formation).This system includes the structure of the brain stem, which are suitable branches of the sensory nerve tract, leading from the spinal cord to the cortex.However, the exact mechanism causing sleep has not yet been established.Experiments on animals with damage to certain parts of the brain show that it has certain structures that induce sleep and inhibit the reticular system.They are located in the subcortical areas, including the upper part of the brain stem (bridge), its lower parts, and the preoptic region of the hypothalamus.Other similar studies have shown that sleep with rapid eye movements and sleep withoutrapid eye movements are associated with the activities of different structures.So, damage to the dorsolateral region of the bridge tire only suppresses sleep with rapid eye movements, but does not affect sleep withoutquick eye movements.

As it turned out, for the emergence of sleep with rapid eye movements, one of the structures of the bridge, namely the caudal reticular nucleus, is necessary.Its destruction in experimental animals leads to the loss of this phase of sleep in them.Another structure of the brain – the so-called.blue spot – apparently responsible for the appearance of eye movements during sleep with rapid eye movements.